Multiply two powers of the same base by adding their exponents
To find 16 x 64, rewrite them as 2⁴ x 2⁶. Same base, so just add the exponents: 4 + 6 = 10, giving 2¹⁰ = 1,024. Engineers once used printed log tables to do exactly this — converting hard multiplications into easy additions long before calculators existed.
